Corrected TwoWire::onRequestService(void) to correctly reset the write buffer before send frame.

[goodchip]

Hi!

txBufferIndex and txBufferLength is used in TwoWire::write(uint8_t data) of the original ATMEGA328p Wire library for control the iteration of write buffer...

...but no longer control the buffer since TwoWire::write(uint8_t data) is modified for run with megaavr architecture (the new variable for control it is slave_bytesToWrite).

I've modified TwoWire::onRequestService(void) for reset correctly the buffer before than the slave send his datas.

---

This sample code slave side shows the problem: (in using the ATMEGA4809 chip from Arduino Uno WiFi Rev2)

#include <Wire.h>

void setup() {
  Wire.begin(0x10);
  Wire.onRequest(reqIRQ);
}

void loop() {
  delay(1000);
}

void reqIRQ() {
  Wire.write(0x01);
  Wire.write(0x02);
  Wire.write(0x03);
}

1st read on master at 0x10 address:

0x01
0x02
0x03

2nd read on master at 0x10 address:

0x01
0x02
0x03
0x01
0x02
0x03

3th read on master at 0x10 address:

0x01
0x02
0x03
0x01
0x02
0x03
0x01
0x02
0x03

etc.

[facchinm]

LGTM! Merging

[goodchip]

Hello @facchinm, peer validation before merge maybe?

[facchinm]

Sorry for the delay, I was almost sure I pressed the button 😭